Experimental study on the variation characteristics of phase physical properties of Jimsar shale oil gas injection
To explore the phase behavior and physical property change characteristics of shale oil with dif-ferent injected gases,the gas injection expansion experiments of oxygen-reducing air(10％oxygen con-tent),air,and CO2 were carried out by using high-temperature and high-pressure PVT physical simulation experiment system and gas chromatography.By real-time monitoring of the changes in phase behavior of different oil and gas systems,the effects of different injected gases on the physical parameters such as sat-uration pressure,expansion coefficient,viscosity,and density of the formation oil system were analyzed.The results show that the effects of different injected gases on the phase behavior and physical properties of formation oil are significantly different.Low-temperature oxidation(LTO)reaction can occur when air is injected into shale reservoirs in contact with crude oil.The higher the oxygen content in the air,the stron-ger the low-temperature oxidation,the more conducive to the dissolution of the gas phase into the oil phase,and the lower the saturation pressure of the system.When CO2 is injected,it is easy to produce a better miscible effect with crude oil,which can enhance the solubility of the gas.Limited by the higher saturation pressure of dissolution,the expansion coefficient of high oxygen-content air is not much different from that of oxygen-reducing air,but the viscosity reduction effect of high oxygen-content air is more obvi-ous.CO2 Can enter the crude oil under the action of pressure difference and diffusion,and the extraction strength is greater,and the effect of expansion and viscosity reduction is the best.When high oxygen-con-tent air contacts with crude oil,the mass exchange can be generated to extract light components into the gas phase,which accelerates the increase of heavy component proportion and crude oil density.The strong extraction effect of CO2 on low-carbon components can promote the conversion of light components to heavy components,which results in a greater increase in crude oil density.CO2 Injection development is expected to be an effective way to improve shale oil recovery and consider storage.This study can provide a reference for the efficient development of gas injection in shale reservoirs.
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